The Study On Cathode Materials Of Lithium-ion Batteries

The paper"The study on cathode materials of lithium-ion batteries"was supported by: optoelectronic & new energy resources material development from construction project of 211 national key project in Sun Yat-sen university and The State Key Scientific and Technological Projec"tIndustrial Experimental Study of the Production of Lithium Carbonate Concentrate from brine Extracted from Zabuye Salt Lake"(2001BA602B-02)Li-ion battery technology has been much attended by people mainly due to high energy density, long cyclic life, high potential per unit, high power of work, low self-discharge rate, no memory domino effect, no pollution, and bulk is small. Based the commercial permission, as promising cathode materials of lithium ion batteries, the improved performance of DMcT and LiMn2O4 were focused studied in this paper. (一) Among of the cathode materials of lithium ion batteries, DMcT is not only has high theory capacity but also affluent resource, better environment effect, easy preparation, high cyclic reversible capacity and high capacity using rate, and became a promising cathode materials of lithium batteries. The electrochemical performance of DMcT was studied in this present paper of the paper. We improved the redox performance of DMcT with electrocatalyst such as PMOT, PEDOT et al. conducting polymers, because the addition of these conducting polymers can increased the electron conductivity of DMcT, and the conducting polymers hold better catalytic performance. In addition, we controlled the molecular weight of poly-DMcT and improved the stability of cycle performance by organomonothiol Organosulfure compound. A few of new results are followed as:1. The redox kinetics of DMcT is rather slow at room temperature.2. The electric performance of DMcT is not better.3. The redox performance of DMcT was improved by addition of conducting polymers such as PMOT and PEDOT. The cathode peak currents were elevated 1.4times and 4.6times respectively. And the peak separations were reduced 2.0times and 1.1times respectively. The first discharge capacity was elevated from 59mAh/g to 142mAh/g and 167mAh/g.4. The cyclic stability of DMcT was improved by doping organomonothiol Organosulfure compound such as 2-mercaptobenzothiazole. The discharge capacity was decreased 26%, and that of DMcT was decreased 48% after eighty cycles.5. The cyclic stability of DMcT/PMOT and DMcT/PEDOT composite were improved by adding organomonothiol Organosulfure compound such as 2-mercaptobenzothiazole.(二) Among of the inorganic cathode materials of lithium ion batteries, spinel LiMn2O4 and layer LiCoO2 are much studied. As cathode materials, LiMn2O4 can be able to bear excessive discharge charge, safety, low cost, relatively high specific capacity and non-toxic, so it is the most promising cathode materials. Though LiMn2O4 has these merits, it shows quickly capacity fading with cycling especially at elevated temperature, and LiCoO2 shows better high temperature stability at high temperature. However, in electrolyte, the surface film formed on the surface of electrode active materials particles is the mostly reason that lead to above defects. The surface film was the reactant that the electrolyte reacted with active materials powder. In this part, we studied the form mechanism, characteristic and component of the films on the surface of LiMn2O4 and LiCoO2 particles, and the effect of electrolyte on cathode materials. In view of the above results, we improved the performance by coating a LiCoO2 film on the surface of LiMn2O4. Furthermore, we also improved the performance by doping cation/anion to LiMn2O4. A few of new results are followed as:1. Compared with LiCoO2,the anti-corrosive ability, cyclic performance at higher temperature and thermal stability of LiMn2O4 were not better;2. The films on the surface of active materials particles is the reactant that electrolyte reacted with metal cation of surface powder electrode, and the component is organic salt.3. Through coating a LiCoO2 film on the surface, the anti-corrosive stability and thermal stability of LiMn2O4 were much improved, so the cycling performance was improved specially at high temperature.The discharge capacity of LiMn2O4 was decreased 26%, and that of LiCoO2-coated LiMn2O4 was decreased 3% after fifty cycles.4. The performance was improved by doping cation/anion to LiMn2O4; The discharge capacity of LiMn1.95Cr0.05O3.95F0.05 and LiMn1.95Cr0.05O3.95Cl0.05 was decreased 6% and 18% after hundred cycles.